In recent years, domestic robots such as nursing-care robots or housework supporting robots are being actively developed. Further, as to industrial robots, robots that cooperate with persons are being actively developed due to spread of cell production plant or the like. Since such robots that cooperate with persons should live together with persons differently from conventional robots that operate in robot task areas separated from human areas, such robots requires safety that is different from the conventional industrial robots.
Further, as to robot arms as one example of robots, an output torque of each joint is calculated based on conveying objects, their self-mass, and inertia moments. Since the torque required by each joint changes between when an object is gripped and when the object is not gripped, a desired torque needs to be suitably changed according to whether the objects are gripped.
However, when an object is gripped in a still state, the mass and the inertia moment are switched between the two states including the gripped state and the non-gripped state. For this reason, the output torque is switched, and a robot arm moves in some cases despite the still state of the desired position of the robot arm. This might damage a gripped object and might cause drop and tumbling of the gripped object or the like, thereby causing a problem from a viewpoint of the safety.
In contrast to switching a mass and an inertia moment in a robot that grips an object, Patent Literature 1 discloses a control device that does not make a calculation by switching a mass and an inertia moment but adds a feed forward term to control a robot (See Patent Literature 1)